More Portland-area homeowners dug their way out from underwater mortgages in the year's first quarter with a boost from rising home prices.

According to the real estate website Zillow, 14.9 percent of metro homeowners with a mortgage owed more on their home than their mortgages were worth. A year ago, 22.3 percent of mortgaged homeowners were under water.

That number has been falling steadily as home prices rise. The number of underwater homeowners has been more than cut in half since "negative equity" peaked in 2012.

Underwater mortgages were a primary driver of foreclosures in the housing crash. When prices fell below the amount owned on the mortgage, homeowners who lost all or part of their income couldn't bail out of a mortgage by selling the home.

Underwater and near-underwater mortgages are still weighing on the housing market and helping drive prices higher. Homeowners whose mortgages are no longer underwater may still be unable to selling their home due to transactional costs and the need for a down payment on their next home.

"It's hard to overstate just how much of a drag on the housing market negative equity really is, especially at the lower end of the market, which represents those homes typically most affordable for first-time buyers," said Zillow chief economist Stan Humphries. "Negative equity constrains inventory, which helps drive home values higher, which in turn makes those homes that are available that much less affordable."

Among the lowest-priced one-third of Portland-area homes, 24.2 percent are underwater, compared with 11.7 percent of middle-tier homes and 7 percent of top-tier homes.